The present invention relates to two-sided printing of sheet material, and more particularly to an apparatus and method for two-sided printing of a sheet-like substrate in a continuous single-pass conveyor-type process.
Various sheet-fed printing systems are known for printing or photocopying text or graphical images on a recording substrate such as a paper or polymer sheet. Many of these systems include means for two-sided printing that involve mechanisms for turning the sheet that has been printed on one side by a printing device and passing the sheet through either a second printing device or the same printing device that was used to print the first side of the sheet. These mechanisms typically utilize a combination of one or more drums, rollers, cylinders, gears, levers and/or sheet guides to turn the sheets. In recto/verso printing devices, these transport mechanisms typically involve bending and manipulating the sheets through a series of drums or rollers.
For example, U.S. Pat. No. 5,964,153 describes a turning device for sheet-fed printing presses that utilizes a turning mechanism that accepts a sheet from the end of a printing path and re-feeds the sheet in an opposite direction into the beginning of the printing path, thereby turning the sheet for printing on a second side. This device requires the sheet to be fed through the same printing path twice. This device also utilizes a plurality of rollers and drivers to move the sheet through the device.
Another example is U.S. Pat. No. 5,233,401, which describes a two-sided printing apparatus that utilizes a sheet re-feeding unit. In this device, a sheet is printed on one side by a printing unit and is re-fed through the device in order to print a second side of the sheet.
While these devices tend to be more suitable for duplex printing of relatively thin sheets in photo-imaging systems and computer printers, they are not conducive to commercial sheet-fed printing systems for duplex printing of thicker sheets or substrates in a continuous single-pass process. These mechanisms are not capable of turning and manipulating thicker printing substrates that tend to be rigid and more suitable for flat conveyor-type printing arrangements. Furthermore, these mechanisms are typically more complex and tend to be more expensive. Such mechanisms are also not practicable to implement in a continuous single-pass flat conveyor-type printing process for industrial and commercial applications.
While single-pass two-sided printing devices have been provided in rotary printing arrangements for commercial printing (e.g. U.S. Pat. No. 5,467,710, which describes a rotary printing press for two-sided printing of sheets that involves passing the sheet through a rotary printing press having two printing units including plates and impression cylinders), a single-pass two-sided printing apparatus in a flat conveyor-type printing arrangement is not presently known. Existing two-sided printing processes that utilize this type of arrangement typically require a substrate to be processed two or more times through the same apparatus. This has a significant effect on production cycle times.
Therefore, it is an object of the present invention to provide an apparatus and method for single-pass duplex printing of a sheet-like substrate in a flat, continuous, and substantially in-line printing arrangement.
It is also an object of the present invention to provide an apparatus and method for duplex printing of a sheet-like substrate that utilizes a simple and economical sheet-turning arrangement to allow for two-sided printing of a sheet-like substrate in a flat, continuous, and substantially in-line printing arrangement.
It is a further object of the present invention to provide an apparatus and method for duplex printing of a sheet-like substrate that is economical and conducive to commercial and industrial printing applications.
These and other objects will become readily apparent after reviewing the specification and drawings.
The present invention is an apparatus and method for duplex printing of a sheet-like substrate in a continuous single-pass flat printing process. The device comprises a first conveyor unit in communication with a feeder and a second conveyor unit in communication with a delivery. Each conveyor unit has a printing device and a drying/curing device disposed adjacent to the conveyor unit. A transfer device is disposed between the two conveyor units for transferring a substrate from the first conveyor unit to the second conveyor unit. As a substrate is conveyed on the first conveyor unit from the feeder, a first printing unit prints a first side of the substrate. A first drying/curing device dries or cures the material printed on the first side of the substrate. The transfer device turns the substrate over as it transfers the substrate to the second conveyor unit to expose a second side of the substrate to a second printing device disposed adjacent to the second conveyor unit. A second drying/curing device dries or cures the material printed on the second side of the substrate. The second conveyor unit conveys the printed substrate to the delivery. Alternate embodiments may include additional conveyor units to facilitate relative positioning of the elements of the apparatus or to facilitate further processing of the substrates at other locations.